1. Field of Invention
The present invention relates to a current sensor and, in particular, to a passive alternating current sensor.
2. Related Art
In industries, the current detection is usually applied to the applications of system over-current protection and current control, such as power decay detection, motor overload detection and protection, current mode control for power source, and control system diagnosis.
The conventional current sensors include contact or non-contact sensing methods. The contact sensing method is to configure a sensing circuit for measuring the resistance, inductance, capacitance, or voltage between two ends of the transistor, and then to calculate the sensing current. The non-contact sensing method is to sense the magnetic field around and generated by the current-carrying conductor by the current transformer method, Hall element method or magnetometric resistivity method. Otherwise, the non-contact sensing method may obtain the sensing current by measuring the variation of mechanical energy converted from magnetic energy. The above-mentioned contact and non-contact sensing methods have their respective advantages and disadvantages, and they may be suitable for different applications.
As shown in FIG. 1, a conventional current sensor for detecting the mechanical energy converted from the magnetic energy includes a coil 11 for carrying current, a pressure-resistance element 12, and an MEMS structure layer 13. The coil 11 and the pressure-resistance element 12 are disposed on the MEMS structure layer 13. The coil 11 is located within the magnetic field generated by the current-carrying conductor CC, so that it is subjected to the Lorentz force and applying a force to the MEMS structure layer 13 as well as indirectly to the pressure-resistance element 12 through the MEMS structure layer 13. Accordingly, the impedance of the pressure-resistance element 12 is decreased so as to generate a voltage drop, so that the current value of the current-carrying conductor CC can be obtained. Since the conventional current sensor 1 is a non-contact current sensor, it can prevent the current-carrying conductor CC to be detected from influence and can avoid high power consumption under the detection of the system with large current and power.
However, as mentioned above, the conventional current sensor 1 is an active current sensor, so that the power must be applied to the current sensor 1 for operation. Besides, during the sensing process, once the current flows through the current-carrying conductor CC, the current sensor 1 is always on duty. Thus, the MEMS structure layer 13 must bear the most reciprocating force all the time, so that it is easily out of function due to fatigue and aging. In order to enhance the sensitivity of the current sensor 1, the coil 11 wound with a lot of rounds is configured on the MEMS structure layer 13. However, the power consumption of the coil 11 may cause the MEMS structure layer 13 to generate heat so as to increase the temperature and generate heat stress, which may affect the operation of the current sensor 1.
Therefore, it is an important subject of the present invention to provide a passive alternating current sensor that can perform desired sensing process without being applied by electricity. Besides, the structure layer thereof can resist the fatigue and aging problems, and can prevent from generating heat, which affects the sensing procedure, due to the configured coil with a lot of rounds.